1. Field of the Invention
The present invention relates to an electrostatic printing device for reproducing information, and more specifically to an electomagnetic printing device.
2. Description of the Related Art
A electromagnetic printing device of the kind herein under consideration is known from U.S. Pat. No. 4,884,188. The wall thickness of the electrically conductive sleeve of the magnetic roller of the printing device disclosed therein must be as thin as possible in order to minimize any distortion of the magnetic field in the image-forming or image-development zone. However, a thin wall-thickness for the magnetic roller sleeve means that the roller is of relatively low rigidity so that the sleeve vibrates during rotation. Such vibrations cause changes in the distance between the surface of the sleeve of the magnetic roller and the image-forming element of the printing device at the image-forming zone therebetween so that the magnetic toner brush formed there by the magnetic developer powder does not remain satisfactorily in position. This results in lack of uniformity in image-development. Also, the degree of sleeve vibration varies over the length of the magnetic roller so that the magnetic toner brush does not extend rectilinearly transversely of the direction of transport of the image-forming element, but extends along a curved line continually changing shape. As a result, the toner particles of the developer powder do not reach the image-forming element at the correct location, and this is visible as image defects on the copy.